The field of this invention is turbochargers of the type used to provide pressurized combustion air to an internal combustion engine. More particularly, this invention relates to a turbocharger including a housing journaling an elongate shaft for rotation with a turbine and a compressor. The turbine and compressor are spaced apart at opposite ends of the shaft, and the housing defines a closed void substantially surrounding the shaft. A quantity of material having selected heat transfer and heat absorptive qualities is disposed within the closed void for controlling the temperature of both the shaft and housing bearings following engine shutdown.
Turbochargers in general are well known in the pertinent art for supplying pressurized combustion air to an internal combustion Otto or Diesel cycle engine. Historically turbochargers have been used on large engines for stationary or heavy automotive farm or construction vehicle applications. These turbocharges generally include a housing including a turbine housing section for directing exhaust gases from an exhaust inlet to an exhaust outlet across a rotatable turbine. The turbine drives a shaft journaled in the housing. A compressor is driven by the shaft and spaced from the turbine housing section. A compressor housing section receives the compressor and defines an air inlet for inducting ambient air and an air outlet for delivering the air pressurized to an inlet manifold of the engine.
Because these past turbocharger applications involved relatively low specific engine power outputs with relatively low exhaust gas temperatures and infrequent engine shutdowns no special precautions were necessary to cool the shaft and the bearings journaling the shaft. Experience showed that the usual engine pressure oil flow lubrication which was necessary during turobcharger operation also by its cooling effect maintained the shaft and bearings at a temperature low enough to prevent oil coking in the turbocharger after engine shutdown. Because the operating temperature of the hot turbine end of the turbocharger was low enough and the mass of the turbocharger relatively large, the highest temperature experienced at the shaft and bearings after the oil flow was stopped was not high enough to degrade or coke the oil remaining in the turbocharger after engine shutdown.
However, passenger car automotive turbocharger applications have brought to light many problems. The specific engine outputs are usually higher leading to higher exhaust gas temperatures. The turbocharger itself is considerably smaller than its heavy equipment predecessor so that a smaller thermal mass is available to dissipate residual heat from the turbine housing section and turbine after engine shutdown. The result has been that heat soaking from the turbine housing section and turbine into the shaft and remainder of the housing raise the temperature high enough to degrade or coke the remaining oil in the housing after engine shutdown. Of course, this coked oil may plug the bearings so that subsequent oil flow lubrication and cooling is inhibited. This process soon leads to bearing failure in the turbocharger.
An interim and incomplete solution to the above problem was provided by the inclusion of a hydraulic accumulator with a check and metering valve in the oil supply conduit between the engine and turbocharger. During engine operation this accumulator filled with pressurized oil. Upon engine shutdown the oil was allowed to flow only to the turbocharger at a controlled rate to provide bearing and shaft cooling while the remainder of the turbocharger cooled down. However, the frequent shutdowns and restarts to which automotive passenger vehicles are sometimes subjected does not allow sufficient time for filing of the accumulator. Under these conditions failure of the turbocharger may be accelerated.
Another more recent and more successful solution to the above problem has been the provision of a liquid cooling jacket in a part of the turbine housing adjacent to the turbine housing section. Liquid engine coolant is circulated through the jacket during engine operation by the cooling system of the engine. Following engine shutdown the coolant remaining in the jacket provides a heat sink so that residual heat from the turbine housing section does not increase the shaft and bearing temperatures to undesirably high levels. U.S. Pat. Nos. 4,068,612 of E. R. Meiners, and Re. 30,333 of P. B. Gordon, Jr., et al, illustrate examples of this conventional solution to the problem.
However, this latter class of turbochargers all require that engine coolant be piped to and from the turbocharger. This is usually accomplished with flexible hoses which complicate and increase the cost of the original installation of the turbocharger. Also such plumbing requires additional maintenance and may be subject to coolant leakage which could disable the vehicle.